Copper-sulphur alloy



Dec. 14, 1937.

c. s. SMITH COPPER-SULPHUR ALLOY Filed Sept. 21, 1953 EFFECT OF SULPHUR 0N MACHINABILITY OF COPPER (HARD DRAWN) 3 2 ham: 3 5 55 2093 0 SULPHUR PER CENT.

INVENTO TTORNEY$ retested nee. 14, 1937 CQPPER- SULPHUR ALZLQBY Cyril Stanley Smith, @hcshirc,

to The American Brass Company,

Conn, assignor Waterbury,

Conn, a corporation of Connecticut Application September Zll, 1933, Serial No. 69,35

8 Cllaims. (Oi. i5-1t'$ii) I with SuhJllur and I have hot rolled alloys contaim- My invention concerns a series of alloys of copper distinguished by a remarkable ease of machining. The free-cutting properties are achieved without great sacrifice of strength or ductility by additions of sulphur to pure copper or to a number of copper base alloys containing other elements. In many cases the other elements of sulphur family, i. e., selenium and tellurium, can be used in combination with sulphur.

The figure of the drawing shows a curve indicating the eifect of sulphur on the machinability of copper.

One of the principal objects of the refining operation as applied to the production of metallic copper from the crude matte is to remove from the metal the elements of the sulphur family. Almost without exception these elements have been hitherto regarded as extremely harmful to the malleability and ductility of copper in both the hot and cold conditions, and for this reason have been rigorously excluded. On account of this long-held opinion as to their deleterious cf"- fects they have not been subject to careful study in recent years and their true influence on copper has remained unknown. In my researches I have found that none of these elements in reasonable amounts are harmful to the hot and cold working properties of copper and that they all render the metal particularly readily cut with edge tools and very suitable for the manufacture of parts on so-called automatic screw machines or by any customary machining operations.

Sulphur may be added to copper alloys either with the cold furnace charge or it may be added to the molten alloy in the form of the element or as CllzS which is soluble in molten copper to the extent of about 1.5 per cent. sulphur. On account of the volatility of the element and the poisonous nature of its fumes the latter method is to be preferred. A eutectic is formed at a temperature of about 1070 C. containing approximately 1 per cent. sulphur. Beyond approximately 1.5 per cent. further additions of sulphur cause the formation of drops of Cues which tend to float out of the alloy during melting or solidification. Small amounts of sulphur form eutectic areas filling in the spaces around the primary copper grains and the amount of eutectic increases with sulphur additions. The eutectic of copper and CuzS is very similar in microscopic appearance to the copper-copper oxide eutectic so familiar to metallurgists, and has even less effect on the hot working properties. The addition of other elements to binary copper-sulphur alloys usually coarsens the particles of CuzS in the eutectic but, except in some special cases which will be discussed later, does not otherwise modify the structure.

Contrary to the general impression, I have found that it is possible to forge copper saturated v ing up to 1.0 per cent. sulphur with no difliculty whatever, even using the severe reductions in a rolling mill designed for the commercial rolling of copper wire bars. Alloys containing up to this amount and larger amounts, of sulphur may be cold rolled, drawn or fabricated in any manner involving either hot or cold working with no particular precautions.

The alloys may also be used in the cast condition without fabrication. As with any copper alloy, it is advisable to melt and cast with exclusion of oxygen or with the addition of a deoxidizing element in sufficient quantity to combine with the oxygen present in the melt or absorbed from the atmospheric air during pouring. I have used both methods to obtain castings from copper-sulphur alloys and have obtained ingots with a deep shrinkage cavity, which, after feeding, were perfectly sound.

Alloys of copper containing appreciable amounts of sulphur whether in the cast or fabricated condition are characterized by extremely high ma chinability. As is well known, copper is one of the most difficult metals to machine, since its soft and tough character causes it to form long turnings which stick to the tool and absorb much power which appears as heat. The particles of CuzS in my alloys not only prevent the formation of a long chip, which may foul the tool in certain types of machine operations, but they also lubricate the tool, prevent sticking and reduce to a minimum the power required for the cutting operation and the heat generated. At the same time the tool life is considerable increased and a superior surface finish on the work obtained.

Alloys of copper which are desired to have freecutting qualities are at present made by additions of lead in amounts up to 4 per cent.-or'more, but this while favorably affecting machinability, does so at the expense of reducing the ductility, limiting the amount that the alloys can be .cold rolled and entirely preventing hot rolling, at the same time rendering the alloys susceptible to firecracking when annealed after cold working. Additions of sulphur in certain amounts are quite as effective as lead in improving the machining qualities of the alloys and are quite without effect on the hot working properties. The alloys moreover remain entirely immune from fire-cracking under severe conditions of strain and rapid heating.

Additions of sulphur to copper have very little effect on the electrical conductivity and the alloys should find considerable application in the manufacture of electrical devices where high electrical conductivity is necessary in a part which can be made on a high speed automatic screw machine or for parts such as bus bars which sometimes .and results in rather poor properties when the metal is tested transversely to the direction of rolling, but an annealing or soaking operation enables the strings of sulphide to break up into more or less rounded globules which have comparatively little effect on the ductility in any direction. Due to the'lower ductility of the base metal, the poor transverse properties due to the long thin fibers of sulphide are more marked in alloys containing other elements, for example, silicon, nickel or tin, in addition to the sulphur than they are with pure copper-sulphur alloys. To show the erroneous nature of the common conception that sulphur renders copper brittle, 1 have given in Table I the tensile properties and electrical conductivity of some copper-sulphur alloys which were melted and cast in 3 in. diameter ingots and then hot rolled to in. and cold drawn to A in. diameter, at which size the tests were made. I tests on the. same alloys after annealing at 600 C. This temperature was not suiliciently high to spheroidize completely the CmSflbers, and higher ductility would have resulted had the annealing been more drastic. The amount of sulphur in ,these testswas limited to 1.0 per cent., since preliminarytests showed this 130 be all that could easily be retained and was suillcient for the purpose in view. However, .sulphur can be added in amounts up to the limit 01' liquid miscibility, which is about 1.5 percent, without destroying the ductility of copper.

TABLE I Tensile properties and electrical conductivity of cold drawn and annealed copper-sulphur alloys The table also includes results of drawn copper under light loads as it is under normal cutting pressure, neither, according to my preliminary experiments, does an addition of less than 0.25 per cent. sulphur improve the ease of cutting the alloys when these are in the annealed condition.

Sulphur is not as effective as the related elements selenium and tell'urium in affecting the machinability, but its lowcost renders it an at.--

tractive additioh inv cases where the greatest machinability is not required. To secure a ma--' terial improvement in machinability sulphur should be added in amount from approximately 0.05 per-cent. up to about 1.5 per cent., but the preferred range is from approximately 0.25 per cent. to 1.0 per cent.

The following table determined from tests shows the eflect of sulphur on the machinability of hard drawn copper.

I TABLE II Machinability of copper-sulphur alloys (Hard drawn) Machin- Alloy Per cent. abmt Y No. sulphur index.

1001 o. o 253 1616 0. 15 165 1602 0. 23 120 1611 0. 54 95 164B 0. 78 86 1613 0. 97 86 Yield point Elonga- Reduc- Conductiv- A110 Composl- 0.5 cent 2% tlon tion of ity I.A.C.S. No. tionperoent lbe./ I in in 1.4 area per cent,

I in. per cent per cent 20 C.

, Cold drawn 1M1 99.99 Cu 50, 550 52, ill 21. 1 87. 4 99. 7 1515 0. 15 S 50, am 52, 100 15. 7 56. 4 W. 8 1002 0. 23 B 51, 450 52, 650 13. 9 50. 2 97. 6 1611 0. 54 B 52, 450 250 12. 4 38. 1 95. 1 1608 0.788 53,050 55,250 7.5 19.1 91.6 1013 0.91s 53,750 50,250 8.7 32.0 00.0 s Annealed 1 hour at 000 0.

1601 W. Cu 9,285 32,550 58.6 92.3 102.1 1616 0. 15 S 8, 245 32, 950 53. 2 72. 6 99.3 1602 0. 25 B 7, W 53, 100 52. 9 67. 3 99. 5 1511 0. 54B 10, 225 33,5!) 50. 8 59. 95. 7 I 0.783 10,950 85, 44.3 42.7 92.5 1613 0.97 S 11,M 35,050 44.7 47.8 91. 4

These alloys were hot rolled from 3 in.. to 0.5 in. in one pass. Gauge length 0! test piecu o. in. diameter.

To demonstrate the remark ble ease of machining the alloys, I have rep need in Figure 1 the results of some crude drill tests: This curve shows the number 01' turns necessary for a drill 0.25 indiameter to penetrate 0.35 in. into the metal under the load shown. Sulphur is not as emcient in improving the machinability of hard 0.625 in, annealed and cold drawn to Copper alloys with silicon in all proportion, but there is useful ductility only in the range up to approximately 5 per cent. silicon. These alloys find considerable application in industry, usually in combination with some other element to improve the strength or'otherwise modify the properties. I have studied alloys of copper containing oi turns of a 0.25 in. drill Table III also includes a corresponding to the TABLE III An alloy containing to per cent. silicon,

0.05 to 1.5 per cent. sulphur, 93 to 99.95 percent. copper. I

An alloy containing approximately 4.0 per cent. silicon, approximately 0.5 per cent. sulphur, approximately 95.5 per cent. copper.

An alloy containing 0-5 per cent. Si, 0-11 per cent. Fe, 0-10 per cent, Zn, 0.05-1.5 per cent. S, the balance being principally copper.

An alloy containing approximately 3.5 per cent.

Tensile properties and. machinability of cold drawn and annealed copper-silicon alloys containing sulphur Composittion E1 I R a percen Yield point Tensile qngg' e Machinll? ,g-n sga e sit in e g s. sq. in. s. sq. in. psrcnt percent in ex 1! Silicon phur l l l Cold drawn Annealed 1 hour at 750 c.

v 1628 3. 79 U. 0 20. 400 61, 050 70. 7 67. 8 192 1825 3. 73 0. 10 27, 950 65, 050 60. 8 63. 0 188 1624 3. 75 0. 26 29, 100 64, 200 59. 7 57. 3 154 1623 3. 86 Y O. 45 30, 100 62, 750 52. 5 40. 2 99 These alloys were hot rolled from 3 in. to 0.625 in, annealed and cold drawn to 0.5 in. in two passes. Gauge length of test pieces-0.357 in. diameter #The machinability index represents the number of turns of 0.25" drill to penetrate 0.25" into the alloy under a load 0! 86 pounds.

Most of these copper silicon alloys as commercially produced contain also additional elements which serve to improve the properties in various ways and new copper alloys will undoubtedly be developed in the future based on these or entirely new combination of elements. Sulphur may be added to any complex copper alloys with as much facility as to the binary alloys unless there is present a large amount of some element which combines with sulphur and forms a sulphide which is not soluble in the liquid alloy. When this occurs sulphur is rapidly eliminated and does not remain evenly distributed throughout the casting. Among the common elements which do not prevent the retention of sulphur in the alloy, I have found the following: Fe, Sn, Sb, Ag, P, Cd, Si, Ni, while the elements Al, Mg, Ca, Zr, and Mn if present in more than a small quantity tend to eliminate the sulphur, while zinc if present in more than perhaps per cent. has a similar efiect. In the case of manganese, amounts up to 0.5 per cent. are permissible, although 1.0 per cent. causes segregation of sulphur. For all those elements which combine with sulphur more avidly than does copper, there will be a limiting concentration below which the insoluble sulphide will not form and the sulphur will remain distributed uniformly throughout the alby, but above which concentration the sulphide is insoluble in the liquid state.

Some of the alloys with sulphur which are of importance include the following copper base alloys containing from 0.05 per cent. to 1.5 per cent. sulphur.

An alloy containing 0.05 to 1.5 per cent. sulphur, the balance being principally copper with additions of up to five per cent. silicon and one or more of the following elements: 0 to per cent. zinc, 0 to 20 per cent. nickel, 0 to 5 per cent. iron, 0 to 15 per cent. tin, 0 to 2 per cent. cadmium.

. visable to use additions of Si, 2 per cent.'Fe, 2 per cent. Zn, 0.5 per cent. S, the balance being principally copper.

An alloy containing 0-5 per cent. Si, 0-10 per cent. Sn, 0.05-1.5 per cent. S, the balance being principally copper.

An alloy containing approximately 1.75 per cent. Si, 1.0 per cent. Sn, 0.5 per cent. S, the balance being principally copper. I

Alloys containing 0 to 5 per cent. silicon, 0 to 10 per cent. zinc, 0 to 5 per cent. tin, 0.05 to 1.0 per cent. sulphur, the balance being principally copper.

An alloy containing 3.25 per cent. silicon, 1.5 per cent. zinc, 0.5 per cent. tin, 0.5 per cent. sulphur, the balance being principally copper.

The other elements of the sulphur family, via, selenium and tellurium, behave in a manner similar to sulphur and are the subject of my accompanying applications. It may prove adtwo or more of these elements simultaneously and it should be understood that whenever sulphur is mentioned in this specification, sulphur with more or less of the elements selenium or tellurium, or selenium and tellurium may be included.

It is also possible to add sulphur or a suitable sulphide to alloys made by the process of compressing powders and sintering at a temperature below the melting point. In this case there is no limit to the alloys with which sulphur can be combined, for the lack of solubility in the liquid state is of no importance.

The lubricating nature of the copper-sulphide as shown by its action on the cutting tool suggests that the alloys containing sulphides would be useful for bearing purposes.

Having thus set forth the nature of my in vention, What I claim is:

1. An article of manufacture for use in machining operations formed of a. copper base alloy which is workable hot and cold, containing silicon in appreciable amount up to 5%, and to which free cutting" properties are imparted by the incorporation of from 0.05% to 1.5% sulphur.

2. An article of manufacture for use in machining operations formed of a copper base alloy which is workable hot and cold, containing silicon in appreciable amount up to 5%, and to which free cutting properties are imparted by the incorporation of from 0.25 to 1% sulphur.

3. An article of manufacture for use in machining operations formed of a, copper base alloy composed of silicon in appreciable amount up to 5%, sulphur from 0.05% to 1.5% and balance copper.

4. An article of manufacture for use in machining operations formed of a copper base alloy composed of silicon in appreciable amount up to 5%, sulphur from 0.25% to 1%, and balance copper. v

5. An article of manufacture for use in machining operations formed of a copper base alloy composed of copper, silicon and sulphur, in which the silicon content is about 4%, the sulphur about 0.5% and balance copper.

6. A copper base alloy composed of silicon in appreciable amount up to 5%, 0.05% to 1.5% sulphur, and balance copper. I

'7. A copper base alloy composed of silicon in appreciable amount up to 5%, 0.25% to 1% sulphur, and balance copper.

8. A copper base alloy composed of 4% silicon, 0.5% sulphur, and 95.5% copper.

CYRIL STANLEY SMITH; 

